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Open Access A Computationally Efficient Aerosol Nucleation/ Condensation Method: Pseudo-Steady-State Sulfuric Acid

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In order to model accurately the size and number of atmospheric particles, it is necessary to predict aerosol nucleation rates. However, the explicit prediction of the sulfuric acid vapor concentration may become computationally intensive when nucleation and condensation are simultaneously occurring. In this article, we develop and test a computationally efficient solution to the problem of solving for the sulfuric acid vapor concentration. Rather than explicitly solving the differential equation for the temporal profile of sulfuric acid vapor, we assume that the sulfuric acid vapor is at the concentration in steady state with its source (oxidation of SO2) and sinks (condensation and nucleation); this is known as the Pseudo-Steady-State Approximation (PSSA). Two versions of a box model with online size-resolved aerosol microphysics were developed to test the PSSA; (1) a “benchmark model” that solves explicitly for the sulfuric acid vapor concentration, and (2) a “PSSA model” that uses the PSSA. A wide array of atmospheric conditions was used to compare the benchmark and PSSA models. The mean difference in the total number of particles in the two models with diameters larger than 10 nm was only 1.8% and 1.1% in lower troposphere simulations after 2 and 6 hours, and 3.8% and 2.3% in the upper troposphere simulations after 2 and 6 h. The PSSA model was faster in 97% of the tests, more than ten times faster in 91% of the points, and more than 100 times faster in 69% of the tests.
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Document Type: Research Article

Affiliations: Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA

Publication date: 01 March 2009

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